Yeah, we totally need to have a Warframe with a Nullifying aura that will nullify itself and your surrounding teammates.
No, honestly, I don't even see the point of adapting an anti-Warframe feature on a Warframe. Would be like adding Fire Protection on your Ignis to prevent it from heating.

Or a permanent option letting you decide on the initial enemy level or rotation count.
For example, you could chose to start Hieracon at the 2k cryotics mark or a Hydron at the 40th wave. Of course you would skip all the "missed" rewards and could only start with the first A rotation, simply at higher level.
For non-endless missions, maybe having the possibility to chose enemy level (capped the same as Simulacrum, based on your MR).

Well, I think the high-level-instancing should be spread solar-system-wide, at all.
We don't need to have only one challenging area. I want to do challenging runs on Venus, Saturn, Earth, Lua, EVERYWHERE.

What about Light giving buff or whatever advantage with Primes and Dark for Umbras
Regarding the Sacrifice part, I'm not 100% convinced it is necessarily someone who'll die. It can perfectly another kind of Sacrifice. Perhaps we will sacrifice our freedom to definitely bind ourselves to one Warframe. That'd just be lore-wise of course, you'll still be able to play with everything in your Arsenal, but maybe you'll be able to only have one Umbra at a time, and the Umbra Warframe may be mandatory for a dedicated mission-type.

There are several problems with Hydron.
First, Riven. Lots of people will chose Hydron for the "Defense mission without pods taking damage" challenge. Even though they don't realize this challenge is 700% times easier in solo due to the fact there are 5 enemies per wave.
Second, TWW that required Sedna to be unlocked. Lots of players moved from Helene to Hydron.
Third, and that's a general defense issue, late-leavers. Especially when it's the Host who leaves, that will completely leave the mission bugged with enemies stuck in their spawns.
Fourth, general issue as well, people leave at 5 if the powerleveling is not fast enough. I admit that sometimes I tag in Hydron with everything unranked so I can't kill stuff efficiently or really fast. And when the complete squad is like that, that's better to retag hoping to be grouped with a Saryn or whatever.